Launch Test Director Jeff Spaulding said yesterday: "I'm very happy to report that we are tracking no problems and the vehicle is in great shape."

There's a four-hour launch window between 12:00 and 16:00 GMT, although NASA estimates a "40 per cent chance that the weather on Tuesday morning will cooperate". If it doesn't, NASA will go for a launch on Wednesday, during the same time frame.

The test flight - featuring a dummy upper stage - will allow NASA to "test and prove flight characteristics, hardware, facilities and ground operations associated with the Ares I". The first stage solid rocket boosters will carry the Ares I-X to an altitude of 40km (25 miles). The booster stage will parachute into the Atlantic for recovery, while the dummy stage will come down with an almighty splash.

NASA remains upbeat about the Constellation programme, despite growing criticism of the project. Following the release of the final report (pdf) of the committee tasked with reviewing the future of the US's human spaceflight programme, chairman Norman Augustine expressed doubts that the Ares I actually serves any useful purpose.

He said of the planned use of the vehicle to supply the International Space Station: "We think NASA would be better served to spend its money and its ability, which is immense, focusing on going beyond low-Earth orbit rather than running a trucking service to low-Earth orbit."